(1) Field of the Invention
The present invention relates to an apparatus for continuous molding of concrete blocks having refractory material coated metal surfaces which mold the concrete blocks. In particular, the present invention relates to metal surfaces which have been flame sprayed with a mixture of a refractory material and a metal binder to provide abrasion resistance and then smoothed. Further, the present invention relates to a preferred polymeric coating of a thermoset polymer applied to the refractory and metal binder coating which provides a smooth surface for molding the concrete blocks.
(2) Description of Related Art
Examples of continuous concrete block molding apparatus are well known to those skilled in the art and are shown for instance by U.S. Pat. Nos. 2,319,291 to Besser, 2,587,413 to VanderHeyden, 2,566,787 to Zevely, 2,985,935 (Re. 25,404) to Wellnitz, 3,608,162 to Staton, 3,832,119 to Woelk, 3,660,004 to Woelk, 3,545,053 to Besser, 4,235,580 to Springs et al, 4,260,352 to Balhorn, 4,395,213 to Springs et al and 4,978,488 to Wallace.
The production rate of a block molding plant is a linear flow which is paced by the block apparatus. When the block molding apparatus is running, the whole plant runs. When it is at rest, the whole plant is at rest. A mold change sequence, being made for whatever reason, usually because of wear on the mold, idles the block molding apparatus and disrupts the flow of the entire block plant for about 35 minutes or longer.
The principal elements of a block plant are as follows: (1) hoppers, bins, and water lines to feed sand, aggregate, cement, and water to the mixture; (2) a mixer and material handling system to feed the cementitious materials to the block molding apparatus; (3) a block molding apparatus producing up to 1,620 blocks per hour; (4) a stacking system to collect and position the green block carried on steel pallets in racks; (5) shuttles to move racks into the kiln; (6) a kiln to cure the green block; (7) shuttles to remove racks from the kiln; (8) a device to remove the cured block and steel pallets from the racks; (9) a depalleter to remove the block from the steel pallets; and (10) a cuber to collect, bundle, and strap the individual blocks for shipment.
The principal components of concrete block (including paver) mold assembly in the block molding apparatus are preferably manufactured of 8620 steel and carburized (case hardened) to 48 to 52 Rockwell, C-scale. This case hardened surface resists both wear and abrasion while still providing a ductile core which allows parts to be straightened after physical part distortions occur in the heat treating process. Surfaces of division plates forming the blocks must be ground before heat treatment to a 125 pin or better micro finish to produce smooth finishes on the faces of the concrete blocks being formed.
A steel pallet (plate) is held against the bottom of the mold by hard rubber blocks. Voids in the mold cavity are filled with cementitious materials and the mold assembly is caused to vibrate by the spinning of eccentric weights located on each end of the mold assembly. The cementitious materials begin to compact under vibration and a plunger is lowered to help compress the materials against the steel pallet by adding additional physical forces to the compacting forces caused by the vibration. Once the proper material density has been reached, as measured by the amount of material fed into the mold assembly, the length of the cycle time, and the measured height of the block, the vibration ceases. The steel pallet and a plunger are then lowered, stripping the block from the bottom of the mold. The pallet carrying the finished block then shuttles out of the apparatus and a new pallet is placed in position and raised against the bottom of the mold assembly. The cycle is then repeated.
Mold assembly wear is caused by the forming, compaction, and stripping of highly abrasive cementitious materials and by metal parts sliding against one another during the cycle and parts coming together during vibration. The wear pattern typical for a concrete block mold assembly is usually about 81/2" (22 cm) up the inside of the mold assembly. Thus, surface wear can occur by friction wherein the materials being vibrated and compacted abrade the surface of the mold or it can occur by impact erosion. In impact erosion, material is displaced from the surface of the mold by physical contact with other components of the mold assembly and the materials themselves being compacted in between components of the mold which are moving in opposite directions and at different rates of speed. This process continues until the surface condition of the mold assembly is unsuited for further use.
In an attempt to create satisfactory molds, solid, tungsten carbide plates, 90 to 100 mils thick, were cast and then bonded to flat surfaces of the mold, and more than a million cycles were completed with no appreciable wear. Coating thicknesses, the cost of the material, and the limitation of casting and applying the coating only on flat surfaces of the mold limited the usefulness of this solution to wear in the mold assembly.
Attempts have been made to increase the surface life of concrete-block molds by applying hard finishes; examples include flame spraying, plasma spraying, and hard chrome plate. Such expedients proved unsuccessful because of material porosity and limited surface adhesion. Other types of surface hardening treatments such as carburizing and nitrating are being used with varying degrees of success.
Udale, U.S. Pat. No. 1,536,952, and Sanborn, U.S. Pat. No. 4,571,983 show flame spray coating of steel working parts with refractory metal in order to increase the number of working cycles they can undergo. It should be noted that these patent disclosures deal with applications in which there is no direct physical contact between surfaces of the mold (e.g. relatively low forces are exerted between the respective surfaces). They disclose examples of materials being molded, pressed, formed, and sheared in dies designed with close fits and running tolerances. In the case of concrete-block apparatus, large mold assemblies and material masses moving in opposite directions and at different rates of speed are subject to abrasion and surface erosion through direct physical contact. This physical contact includes materials very hard in nature and deformation resistant which results in surface material being displaced and rapid erosion of the mold assembly.
Flame spraying of metal parts with metals, alloys and refractory materials to impart wear resistance is well known to those skilled in the art as represented by U.S. Pat. Nos. 1,536,952 to Udale et al, 3,419,415 to Dittrich, 4,262,034 to Anderson, 4,420,543 to Kondo et al. U.S. Pat. No. 2,964,420 to Poorman et al describes the type of coatings which are useful in the present invention, including refractory materials and a binder metal. Such coatings have a high resistance to abrasion, although they tend to be rough and have to be smoothed. U.S. Pat. No. 4,571,983 to Sanborn et al describes a pressure method for smoothing such coatings. Tungsten carbide in a metal matrix is the most well known.
Flame spraying produces the most dense and preferred coating. This coating is described in Product Engineering 59 to 64 (Dec. 6, 1965). One type of equipment is produced by Metco Division of Perkin Elemer, Westbury, N.Y. and the method is described at pages 2.1 to 3.2 with Tables 1 to 7 and is a particularly preferred system.
Fluorocarbon coating materials are known to those skilled in the art. One such material are the Xylan.RTM. materials manufactured by Whitford Corporation, West Chester, PA. These materials are a mixture of an amide thermoset polymer and polymeric tetrafluoroethylene (PTFE). They are known to provide wear resistance. They are described in a Product Bulletin dated Sep. 4, 1990, particularly XYLAN.RTM. 1014/870 Black. U.S. Pat. No. 5,069,937 to Wall also describes the use of polymers containing PTFE for flame sprayed metal coatings to increase corrosion resistance with chromium coatings to provide hardness. The base material can be steel. There is no suggestion in the prior art that such coatings have any use in concrete block making apparatus where smoothness of the surface forming the mold assembly is important.